Oxygen impurities link bistability and magnetoresistance in organic spin valves

Vertical cross-bar devices based on manganite and cobalt injecting electrodes and metal-quinoline molecular transport layer are known to manifest both magnetoresistance and electrical bistability. The two effects are strongly interwoven, inspiring new device applications such as electrical control of the magnetoresistance and magnetic modulation of bistability. To investigate the full device functionality, we first identify the mechanism responsible for electrical switching by associating the electrical conductivity and the impedance behavior with chemical states of buried layers obtained by in operando photoelectron spectroscopy. These measurements revealed that a significant fraction of oxygen ions migrates under voltage polarity, resulting in a modification of the electronic properties of the organic material and of the oxidation of interfacial layer with ferromagnetic contacts. Variable oxygen doping of the organic molecule represents the key element for correlating bistability and magnetoresistance and our measurements provide the first experimental evidence in favor of the impurity band model describing the spin transport in organic semiconductors in similar devices

Stochastic Memory Devices for Security and Computing

With the widespread use of mobile computing and internet of things, secured communication and chip authentication have become extremely important. Hardware-based security concepts generally provide the best performance in terms of a good standard of security, low power consumption, and large-area density. In these concepts, the stochastic properties of nanoscale devices, such as the physical and geometrical variations of the process, are harnessed for true random number generators (TRNGs) and physical unclonable functions (PUFs). Emerging memory devices, such as resistive-switching memory (RRAM), phase-change memory (PCM), and spin-transfer torque magnetic memory (STT-MRAM), rely on a unique combination of physical mechanisms for transport and switching, thus appear to be an ideal source of entropy for TRNGs and PUFs. An overview of stochastic phenomena in memory devices and their use for developing security and computing primitives is provided. First, a broad classification of methods to generate true random numbers via the stochastic properties of nanoscale devices is presented. Then, practical implementations of stochastic TRNGs, such as hardware security and stochastic computing, are shown. Finally, future challenges to stochastic memory development are discussed

Perspective on unconventional computing using magnetic skyrmions

Learning and pattern recognition inevitably requires memory of previous events, a feature that conventional CMOS hardware needs to artificially simulate. Dynamical systems naturally provide the memory, complexity, and nonlinearity needed for a plethora of different unconventional computing approaches. In this perspective article, we focus on the unconventional computing concept of reservoir computing and provide an overview of key physical reservoir works reported. We focus on the promising platform of magnetic structures and, in particular, skyrmions, which potentially allow for low-power applications. Moreover, we discuss skyrmion-based implementations of Brownian computing, which has recently been combined with reservoir computing. This computing paradigm leverages the thermal fluctuations present in many skyrmion systems. Finally, we provide an outlook on the most important challenges in this field.Comment: 19 pages and 3 figure

EMERGING COMPUTING BASED NOVEL SOLUTIONS FOR DESIGN OF LOW POWER CIRCUITS

The growing applications for IoT devices have caused an increase in the study of low power consuming circuit design to meet the requirement of devices to operate for various months without external power supply. Scaling down the conventional CMOS causes various complications to design due to CMOS properties, therefore various non-conventional CMOS design techniques are being proposed that overcome the limitations. This thesis focuses on some of those emerging and novel low power design technique namely Adiabatic logic and low power devices like Magnetic Tunnel Junction (MTJ) and Carbon Nanotube Field Effect transistor (CNFET). Circuits that are used for large computations (multipliers, encryption engines) that amount to maximum part of power consumption in a whole chip are designed using these novel low power techniques

Doctor of Philosophy

dissertationRealization of next generation spintronic devices will require the use of design and engineering of new materials. In order to reach the performance requirements for spintronic transistor devices to become a reality, spin injection must be extremely efficient at room temperature. Understanding new materials and combinations of materials will enable the injection efficiency required for next-generation devices. Rare earth oxides are explored to determine the feasibility of doping magnetic elements to make new dilute magnetic dielectric materials for spin tunneling injection applications. Samarium Oxide (Sm2O3) doped with a small amount of cobalt (Co) is shown to exhibit a magnetic phenomenon which cannot be accounted for by conventional models. Though the observed magnetic properties appear quite similar to those observed in superparamagnetic systems, the origin of these properties is entirely different. A model, based on the widely accepted bound polaron theory for insulating ferromagnets, is proposed to explain the magnetic behavior of Co doped Sm2O3 films. We have also explored the growth and properties of high quality Tb2O3 thin films with on a variety of substrates in preparation for magnetic doping. We show enhanced dielectric constant related to improved crystal quality compared with previous reports, which makes this material of interest in high-k applications as well. Furthermore, we report room-temperature, all-electrical injection and detection of spin-polarized carriers in silicon using NiFe/MgO tunnel-barrier-contacts. From the magnetic-field dependence of the spin-accumulation voltage, spin-lifetime and diffusion-length of the carriers were determined to be 276 ps and 328 nm, respectively. Attaining spin diffusion lengths of >320 nm in Si channels is a ground breaking step and opens tremendous opportunities for integrating spin functionality into post-Moore-era electronic devices. We have carried out similar research with ZnO channels. We report all-electrical injection and detection of spin-polarized carriers in ZnO using NiFe/MgO tunnel-barrier-contacts. The three-terminal Hanle effect is used to study spin transport in single crystal thin film ZnO grown on sapphire. The results show that spin injection persists up to and above room temperature, with a measured lifetime τs=174 ps at 340K. These results underscore the importance of ZnO as a material for future active spintronics devices

Center for Space Microelectronics Technology

The 1990 technical report of the Jet Propulsion Laboratory Center for Space Microelectronics Technology summarizes the technical accomplishments, publications, presentations, and patents of the center during 1990. The report lists 130 publications, 226 presentations, and 87 new technology reports and patents